<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>

<body>
    <script>
        var data = parseInt(prompt("请输入日期数："));
        if (data % 7 == 1) {
            alert("今天星期一")
        } else if (data % 7 == 2) {
            alert("今天星期二")
        } else if (data % 7 == 3) {
            alert("今天星期三")
        } else if (data % 7 == 4) {
            alert("今天星期四")
        } else if (data % 7 == 5) {
            alert("今天星期五")
        } else if (data % 7 == 6) {
            alert("今天星期六")
        } else if (data % 7 == 0) {
            alert("今天星期日")
        }
    </script>
</body>

</html>